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Evolutionary Ecology of Movement Definitions and confusion –Taxes and Kineses –Migration vs Dispersal –Discrete vs. Continuous variation –Philopatry? Evolution –Migratory polymorphisms –Macroptery and habitat persistence Ecology –Metapopulation persistence –Movement response to habitat change
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People break their teeth knowing a great deal about what’s easy, or at least possible, to measure
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Simple movement patterns Taxes –Movements directed towards a goal or stimulus Kineses –Undirected movements (not oriented to a landmark or stimulus) Speed Frequency of turns Angles of turns –Kineses can yield insight on perceptions and state
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Migration vs. Dispersal Migration –Behavioral –Physiological Dispersal –Ecological
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Migration vs. Dispersal Migration –Behavioral Straightened out directed movement Inhibition of responses to normal stopping cues
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The Art of Falconry, Frederick II Hohenstaufen, 1250
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Migration vs. Dispersal Migration –Behavioral Straightened out directed movement Inhibition of responses to normal stopping cues –Physiological Accumulation and mobilization of resources –Fat as fuel
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Fruit is good fuel Parrish 1997, migrants in RI
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Cost of fat in sedge warblers Fuel load = % of lean mass in stored fat
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Migration vs. Dispersal Dispersal –Ecological Increase in the average distance among individual –Opposite of aggregation Movement away from… –Relatives –Population or patch –Competitors TOWARDS… oSuperior habitat oUnoccupied habitat oMates Movement from natal to breeding site or between breeding sites
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Dispersal Definitions Qualitative –Emigration From family From a population or patch –Opposite of philopatry –Costs of leaving or joining a group or territory fitness of residents vs immigrants Quantitative –How far do individuals move? –Do individuals disperse the shortest possible distance Relative philopatry –What is the cost of increased time or distance moved?
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Movement is hard to study Where’d they go? They’re gone? I see one over there Is it philopatric?
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Philopatry? Waser 1985
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Competition? Waser 1985 Ecology 66:1170 Models based on Murray 1967 Hypothesis that animals move the shortest distance possible
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The Problem Dispersal is often measured using mark- recapture on limited study areas The farther an animal travels, the less likely it is to remain on the study area
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Dispersal and survival Survival estimates depend critically on dispersal estimates –Individuals who disappear may have died or dispersed
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Wrentit (Chamea fasciata)
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The palomarin study area
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Observed and corrected dispersal distributions Baker, Guepel and Nur, 1995
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Mean dispersal estimate increased from 268 to 379 meters Juvenile survival estimate increased from 7.3% to 22.9 % Be critical of any claims of philopatry
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How can correction methods be tested? Subsample large study areas, for a start –Cooper et al. used large area from red- cockaded woodpecker –Corrction method worked ok to estimate median movement, less well on variance, survival
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Larger study areas have higher ‘survival’ Zimmerman et al 2007 J App Ecol 44:963-971
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Larger study areas have lower ‘emigration’ Zimmerman et al 2007 J App Ecol 44:963-971
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Evolution of migration Migratory polymorphisms –Migratory vs. Sedentary morphs
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Garden fleahopper
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Migratory syndromes Morphology –Long wings and flight muscles Behavior –Motivation to fly vs. mate Correlated traits –Diapause, plasticity, body size, other life history Polymorphism or Polyphenism
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Megoura viciae, Gilbert “Developmental Biology
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Endocrine mechanisms AJ Zera 2003
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Endocrine mechanisms AJ Zera 2003
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Migratory Tradeoffs Long wings and flight muscles are costly Time spent in migration or migratory condition Mortality during migration –Fitness costs Age at first reproduction delayed Total fecundity reduced
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How do migrants persist?
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Trade off between extinction and colonization R. Denno, in D. Roff 1994, Am Nat 144:772- 798
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Ecology of dispersal
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Persistence of metapopulations Metapopulation - a collection of smaller populations –Each individual population is likely to go extinct –Recolonization from other populations allows the population as a whole to persist
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Persistence depends on dispersal between subpopulations –Survival during dispersal –Willingness to disperse between populations Leave good habitat Cross over poor habitat How are corridors treated?
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Questions How will movement change when habitat changes –Immediate behavior –Evolved response How does migration evolved in fragmented habitat How does migration evolve over the course of invasions?
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Hemilepistus reaumuri
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Desert isopods are detritivores They feed on soil crust,...and dead plants
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Every Spring
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Investigating a burrow
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A new burrow
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Optimality models State space –Current site quality, P(successful reproduction) Strategy set –Remain in current site, or leave to search Optimization criterion –Family survival to following year Constraints –Search and sampling times, range of habitat quality, mortality during searching
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Dynamic programming models Dynamic programming is able to solve problems when fitness depends on timing of actions. Dynamic programming models work backwards from the final time period, so that the later consequences of decisions made now are always known
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Why dynamic programming? Day 11020 Habitat quality
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Fitness if settled Day 11020 Habitat quality Survive to end of season Survive to reproduce
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Fitness if dispersal continues Day 11020 Habitat quality
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Why dynamic programming? Day 11020 Habitat quality
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Why dynamic programming? Day 11020 Habitat quality To solve these questions, start at the end, work backwards Stay
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Fitness is defined as the probability of family survival for a given site quality, x At every time t, is it better to stay or search? F is in terms of fitness at the end of the season, T
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The product of survival until the end of the season and the probability of family survival is mortality, x is site quality, t and T are the present and final days of the season Fitness of settling
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The product of survival until the end of the season and the probability of family survival is mortality, x is site quality, t and T are the present and final days of the season is the probability of ending up in a site of quality x i Fitness of searching
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Habitat quality (probability of breeding) Settle in this range of habitat quality and time Search in this range of habitat quality and time 0 10 20 30 40.52 Time (days) 0 1.04 Be selective early on, even at good sites As the season’s end approaches, be less selective The distribution of habitat quality Model output: The optimal strategy for every combination of time and state
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What does ‘dispersal cost’ an ‘suitable habitat’ mean? Data from 50 years pooled –Distribution of distance or time dispersed –Probability of settling as a function of time of season Proportion settled Time or distanceTime of season Probability of settling
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Incremental costs favor less choosiness / greater philopatry Probability of settling Incremental cost No cost
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Incremental costs create right skewed distributions Proportion settled Incremental cost No cost
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What if sites are ‘suitable’ or ‘unsuitable’? Probability of settling 0 0.2 0.4 0.6 0.8 1 0510152025303540 Distance or day of season Incremental cost No cost Habitat divided into suitable and unsuitable sites
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0 0.05 0.1 0.15 0.2 0.25 0.3 0510152025303540 Distance or time traveled Proportion settled Incremental cost No cost Costs of dispersal only matters if habitat varies continuously Habitat divided into suitable and unsuitable sites
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Simulation results Incremental costs greatly influence dispersal distances and population distributions If only ‘suitable’ and unsuitable sites exist, dispersers must keep moving –Suitable and unsuitable categories are fluid, depend on time of season and costs –Habitat quality is usually a continuous quantity
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An evolutionary scenario Individuals are born with an innate likelihood of settling –Product of selection During dispersal, individuals use their experience to adjust their likelihood of settling –Is this a good year or bad?
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Model conclusions Models with and without learning predict opposite responses to habitat decline –No learning: Dispersal will increase, as individuals search for sites they are unlikely to find –Learning: A decline in habitat will lead to a reduction in selectivity and willingness to search, and no change or a reduction in dispersal
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Two examples of dispersal evolution In fragmented habitat –Pararge aegeria in woodland and farmlands Over the course of an invasion –Frequency of macroptery in bush-crickets
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Two examples of dispersal evolution In fragmented habitat –Pararge aegeria (speckled wood) in woodland and farmlands Merckx et al 2003 ProcB
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Pararge aegeria dispersal Females collected from mostly forested areas and from primarily agricultural and developed areas Reared offspring on cage plants, released adults into 8*30 m outdoor cages –Cages had meadow and woody areas Does fragmentation select for increased movement? –Because resources are more scattered –Because of metapopulation benefits Does fragmentation select for reduced movement? –Because of costs of flying through open areas –Because of costs of changing habitat Merckx et al 2003 ProcB
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Pararge aegeria dispersal (Open bars warm, filled bars cold)
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Bush cricket movement during and following invasion Predictions –Initial founder populations –Subsequent evolution –Think of Roff 1994 Simmons and Thomas 2004 Am Nat
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Bush cricket movement during and following invasion Simmons and Thomas 2004 Am Nat © 2003 Troy Bartlett
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Simmons and Thomas 2004 Am Nat
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Older populations have fewer macropters
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Simmons and Thomas 2004 Am Nat Core populations have fewer macropters Simmons and Thomas 2004 Am Nat
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Core populations have shorter flight range
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Tracking butterfly movements with harmonic radar Ovaskainen O. et.al. PNAS 2008;105:19090-19095 ©2008 by National Academy of Sciences
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Butterflies from new populations traveled farther than those from old (large or small) populations
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Take home messages The best movement work is on butterflies? Evolution of migration is always a multilevel process –Local and short term fitness measures are deceptive Data shapes theory –Costs are hard to measure Especially incremental ones –Quantitative distances are hard to measure –Lots of work on ‘dispersal’ never looks at continuous incremental variation in movement
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Data shapes theory Study areas are limited, static Qualitative questions are much more studied, better understood, than quantitative ones Can technology help? Movebank / Icarus / ARTSI? What is the value of our slice of science? Understanding of behavior, rather than application Current events
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